Internal Combustion Engines and Gas Turbines:
In the 20th century, various types of internal combustion (IC) engines and gas turbines have successfully been developed and been widely used over the years in the stationary power generation, transportation and utility applications. For example, the 2-stroke and 4-stroke engines are used for motorcycle, chainsaw, lawn mower, weed eater, automobile, small power generator etc, the diesel engines are used for truck, bus, stationary power generator etc, and the gas turbines are used for airplanes, power generators etc. Currently, most of the IC engines and gas turbines utilize homogeneous flame combustion of various hydrocarbons (HC) to generate power, and it is known that the timing of ignition, the composition of the fuel/air mixture, the vaporization of the fuels, and the temperature and pressure at the ignition point are very important for a complete combustion. However, despite all the necessary controls and the technology advances over the years, any internal combustion engine or gas turbine will still emit pollutants such as unburned hydrocarbons, CO, NOx, diesel particulates etc.
To reduce the HC, CO, NOx and diesel particulate pollutants from the internal combustion engine's exhaust gas, catalytic converters and/or diesel particulate traps containing supported Pt group metal catalyst have successfully been used commercially for several decades. However, for this pollution removing technology, it is necessary to use an on-board computer as well as various electronic/mechanical devices to reduce the pollutants by controlling precisely the ignition timing, and the air/fuel ratio of the combustion gas. Also, these devices are required to improve the efficiency of the catalytic converters or traps, which are installed in the engine's exhaust pipe lines.
Various other types of IC engines have also been developed successfully in recent years, and these engines can use different fuels such as hydrogen, natural gas, liquefied propane gas, gasoline/ethanol mixture (flex fuel), diesel/bio-diesel mixture etc.
Catalytic Combustion Technology:
Since 1970's, extensive research and development on catalytic combustion technologies have been studied over the years. As demonstrated in U.S. Pat. Nos. 3,975,900, 5,235,804, 5,326,253 and 6,358,040, herein incorporated by references, the catalytic combustion of HC over the supported Pd and other catalysts using various type of reactor designs can reduce the reaction's peak temperature and, thus, can reduce the formation of NOx, while achieving low CO and HC emissions. However, the reaction peak temperatures are frequently found to be exceeding the upper limits of the catalyst, and they would shorten the catalyst life and cause failures during the applications.
In U.S. Pat. No. 6,960,840 to Willis et al, herein incorporated by reference, two catalytic reactors are used with a gas turbine generator to achieve better exhaust emission. Air and natural gas are first compressed and heat exchanged and a primary catalytic reactor is used to raise the turbine's inlet temperature. After the turbine, a second low-pressure catalytic reactor is used to combust the remaining fuels and to recover the heat. But for this primarily catalytic reactor system, water (or steam), CO2 or the recycle exhaust gas are not used in the feed gas to absorb the reaction heats as well as to perform steam reforming and water gas shift reactions. Furthermore, since no precise control of O2/C ratio is described, a sudden momentary increase in O2/C ratio of the feed mixture can cause the run away oxidation reactions over the Pt group metal catalysts, and produce within a few milliseconds excess reaction heats. These heats can permanently deactivate or even melt and destroy the catalysts, and thus reduce the reactor's reliability and its useful life.
Fuel Reforming and Fuel Cells
Fuel cell technologies offer promise and potential as a more efficient, cleaner and quieter process for generating electricity. Therefore, devices using more efficient fuel cell technologies can potentially be used to replace the internal combustion engines for the applications in stationary or mobile power generation, utility and transportation.
However, despite the technology improvements in recent years, every fuel cell technology has limited short operating life, difficult for mass production, and still very expensive and unreliable. For example, the Proton Exchange Membrane Fuel Cell (PEMFC) requires a constant and continuous supply of hydrogen to the stacks (i.e. electrodes) to generate electricity and thus, a reliable source of hydrogen becomes a limitation in this process. Furthermore, fuel cell catalysts are sensitive to some residual hydrocarbons and/or impurities such as sulfur, calcium, magnesium, phosphors etc. and thus, the hydrogen fuel also needs to be purified, a yet further limitation of this process. Another required improvement in fuel cell technology is the seamless integration of the fuel reformer and the fuel cell stack for long hour continuous and reliable operation. For example, a sudden increase/decrease in power requirement can cause flow disturbance to the reformer and thus create unstable operation in the fuel cell stacks.
For fuel cell reforming technology, in U.S. Pat. No. 4,522,894 to Hwang, et al., herein incorporated by reference, hydrogen can be produced from commercial diesel oil by an autothermal reforming (ATR) process, and this reforming process can also be used to generate hydrogen from natural gas, LPG and JP-4 fuels. In this autothermal reforming process, a mixture of #2 diesel oil, water and air is fed into a reformer, which comprises two catalytic zones to yield hydrogen and CO for the fuel cell stack. In the first catalytic reaction zone, the majority of the hydrocarbon (i.e. diesel oil) is reacted over the monolithic palladium and platinum catalyst under very high space velocity (about 10 millisecond contact time) and the feed mixture preferably containing H2O to C ratio of 1.5 to 3.0 and an O2 to C ratio of 0.35 to 0.55.
The main purpose of this reaction zone is to promote catalytic partial oxidation (CPO) reactions to convert most of the feed hydrocarbons into useful CO and hydrogen, and the produced reaction heats can simultaneously be used to raise the feed mixture to a temperature between 600 and 1000° C. for the subsequent second reaction zone. Depending on the O2 to C ratio, either diesel oil or O2 will completely be converted and totally be consumed in this CPO zone. Therefore, at O2/C<0.5, all oxygen molecules are expected to be completely consumed, the diesel oil in the feed mixture can partially (up to 100%) be converted by this CPO reaction to CO and H2, and the % oil conversion can be controlled by adjusting the O2/C ratio of the feed mixture. However, this reaction zone must avoid the complete combustion reactions of hydrocarbons, because the complete combustion reactions at high O2/C ratio>1.0 would produce CO2 and water instead of H2 and CO, and this CO2 cannot be used by most of the fuel cell stacks to generate electricity. In other words, the complete combustion reactions directly convert useful fuels into waste products. Therefore, to improve the fuel cell's thermal efficiency, the optima O2/C ratio in the feed stream to the reformer must be kept within a narrow range, typically between 0.35 and 0.55.
In the second catalytic reaction zone of this ATR technology, the remaining small portion of the unconverted hydrocarbons are reacted with H2O in the presence of a steam reforming (SR) catalyst at 2,000 to 20,000/hr space velocity to yield more hydrogen and carbon monoxide. Since the rate of steam reforming reactions is much slower than that of the CPO reactions, the H2O/C ratio in the feed mixture has a limited effect on the reformer's overall hydrogen production. Thus, this ratio is typically kept below 3.0 without reducing the fuel cell's overall thermal efficiency. In other words, there are almost no advantages of using H2O/C ratio over 3.0 in the feed mixture.
In U.S. Pat. Nos. 6,436,363 and 6,849,572 to Hwang, et al., herein incorporated by reference, the ATR process and the layered Pt group metal catalysts can successfully be used to produce H2 from natural gas or LPG. This ATR process and catalysts have been used in a hydrogen demonstration station as well as in several prototype PEMFC demonstration units for generating electricity from natural gas or LPG.
In addition to U.S. Pat. No. 4,522,894 to Hwang, et al., several U.S. patents such as U.S. Pat. No. 4,844,837 to Heck et al., U.S. Pat. No. 6,254,807 to Schmidt et al., U.S. Pat. No. 7,255,848 to Deluga et al., and U.S. Pat. No. 7,262,334 to Schmidt et al. have successfully demonstrated that the Pt group metal catalysts and the CPO reactions can produce within a very short contact time the CO and H2 from various hydrocarbons, ethanol or other bio-fuels. Furthermore, recent study by Salge et al. (Science, Vol 314, Nov. 3, 2006) had concluded that CO and H2 could be produced from soy oil and glucose-water over Rh—CeO2 catalyst by the CPO reactions.
Fuel Pretreater, Vaporizer and Delivery System:
In U.S. Pat. No. 6,415,755 to Lathi and Johnson, herein incorporated by reference, a plate or a tube fuel processor is used to vaporize the fuel with the hot exhaust gas before injecting the fuel into a combustion source. In U.S. Pat. No. 5,794,601 to Pantone, herein incorporated by reference, a fuel pretreater apparatus and the method for pretreating an alternate fuel for internal combustion engines, furnaces, boilers and turbines are described. In this patent, an engine's by-pass exhaust stream is used to vaporize fuel in a volatilization chamber and also to carry this HC fuel through a heated reactor prior to its being introduced into the fuel burning equipment, such as an IC engine. The reactor is preferably interposed in the exhaust conduit and is formed by a reactor tube having a reactor rod mounted coaxially therein in spaced relationship. The exhaust stream passing through the exhaust conduit provides the thermal energy to the reactor to pretreat the vaporized fuel stream. This fuel processor for pretreating the fuels was later explained by the inventor as a self-inducing plasma generator. In this patent, the Pt group metal catalysts and the catalytic processes were not used to carry out the partial oxidation reactions of the fuels with the recycled exhaust gas, and it did not describe the requirement and necessity of controlling the O2/C, H2O/C and CO2/C ratios of the fuel mixture.
In U.S. Pat. No. 5,947,063 to Smith et al, herein incorporated by reference, a pre-engine catalyst was used to produce synthesis gas (CO and H2) from natural gas for the subsequent IC engine. Portion of the exhaust gas was also re-circulated to the engine together with additional injection of fresh air and natural gas. It was demonstrated that this feed mixture can reduce NOx formation and can improve engine's efficiency. However, though the synthetic gas was produced from natural gas by the catalytic partial oxidation reactions over a monolithic Rh catalyst, this pre-engine catalyst was not installed in the EGR line, and water was not used in the feed mixture. It is known that the addition of water in the feed mixture to the catalytic oxidizer can further reduce or prevent coke formation, which will allow and improve the utilization of various heavier HC as engine fuels. Furthermore, water can also improve the total hydrogen production via water gas shift and steam reforming reactions.
Though some current models of passenger car and diesel truck are equipped with EGR line and some exhaust gas is re-circulated back to the engine for the purpose of reducing the engine's peak temperature and, thus, reducing the NOx emission, there are no commercial on-board catalytic reformers currently installed in the EGR line, and no fuel/water/air mixture injected into this reformer for the purpose of providing hydrogen to assist and to improve combustion's efficiency of an engine or a gas turbine
Plasmatron Fuel Converter:
In U.S. Pat. Nos. 5,425,332 and 7,028,644 to Rabinovich, Cohn et al, herein incorporated by references, a Plasmatron fuel processor can generate electrically conducting gas (plasma) and this plasma gas can initiate non-catalytic partial oxidation reactions of various fuels to produce hydrogen rich reformate for an IC engine. Based on their experiments, the addition of CO and H2 gas to an IC engine's air inlet can increase gasoline engine's efficiency by 20-25%, reduce NOx emission up to 90% and reduce diesel engine's exhaust emission by 90%. Therefore, this plasma on-board reformer for the IC engines offers a cost effective near-term solution to reduce gasoline consumption and CO2 emission. Furthermore, to remove emissions from trucks and buses, this Plasmatron fuel processor can also produce H2 for the purpose of regenerating a NOx or a diesel particulate trap (Bromberg et al, Diesel Engine Emission Reduction Workshop, Newport, R.I., Aug. 24-28, 2003).
However, a fuel reformer containing Pt group metal catalysts has been found to be very effective in carrying out the catalytic partial oxidation reactions of various fuels to produce CO and H2. Therefore, if this catalytic fuel reformer is installed in the EGR line and if it uses the hot exhaust gas to initiate the CPO reactions, this catalytic reformer can effectively be used to replace the non-catalytic Plasmatron fuel converter as an on-board fuel processor for the IC engines, and it can also be used to generate a reducing gas for the purpose of regenerating the NOx and/or diesel particulate traps.
Integrated Catalytic and Turbine System and Process for the Generation of Electricity:
A co-pending application U.S. Ser. No. 11/711,988 was filed on Feb. 28, 2007. According to this invention, a single integrated catalytic and turbine generator or a system combining several single integrated catalytic and turbine generators in series can be used to generate electricity. For example, a fuel mixture comprising the HC (or bio-fuel), steam and an oxygen containing gas are introduced into the reformer and are reacted over a Pt group metal catalyst in a reaction zone to produce a high pressure reformate containing steam, H2, CO, CO2, N2, O2 and unconverted HC. This high-pressure reformate stream can be used to drive a turbine and a generator to produce electricity. However, to improve the durability of the catalyst life, the H2O/C and O2/C ratios of the feed stream must be controlled individually and/or simultaneously so that the temperature in the reactor zone can continuously be kept between 150 and 1200° C., preferably between 150 and 1000° C.
From thermodynamic equilibrium calculations as demonstrated in this co-pending patent application, the addition of water (steam) into the air and fuel feed mixture can reduce the adiabatic temperature, and the reactor can be operated without coke formation in a broader range of O2/C and H2O/C ratios. In addition, due to higher heat capacity, the CPO reactions of the fuels in the presence of steam and CO2 can reduce the reaction peak temperature and thus can improve the durability, life and the performance of the catalyst.
The first reformer's operating conditions of this single Integrated Catalytic and Turbine Generator system can be modified to convert fuels into H2 for an IC engine or a gas turbine. For example, the reformer can be installed in the exhaust gas recycle (EGR) line to produce H2 and CO from the fuels and the hot recycled exhaust gas, and it can also crack catalytically the heavier HC molecules into lighter HC molecules. The produced reformate which comprises unconverted HC, H2 and CO can be admitted into an IC engine or a gas turbine to carry out additional homogeneous or catalytic combustion inside the engine/gas turbine. Since H2 can be combusted more rapidly and cleanly, this on-board EGR Oxidizer can improve the performance of an IC engine or a gas turbine.